Antenna



Aug. 30, 1949. R. E. CLAPP 2,430,182

. ANTENNA Filed Sept. 19, 1945 2 Sheets-Sheet l INVENTOR. ROGER E. CLAPP BY 4 WJ/P-QM Z/AM,

ATTORNEY R. E. CLAPP Aug. 30, 1949.

ANTENNA 2 Sheets-Sheet 2 Filed Sept. 19, 1945 FIG.3.

INVENTOR. ROGER E. CLAPP MM 9. M.

[fie/nay Patented Aug. 30, 1949 PATENT OFFICE alt-tiger 1E. :lClapp, :Gambridge, Mass, assignor, by ;mesne assignments, to the United States of America as represented by-the Secretary of War Application september 19, 1945, Serial"No.' 617-;3-2'2 8'Glaims. 1

Ellis invention relates to .antennae and more matticularlycto. antennae which-radiate circularly polarized electromagnetic .waves.

zlit is irequently desirable "to shave circularly inolari-zed wvaves in electromagnetic :radiationz. 1511011 Radiation ihas sno :clefinite zline 10f vpolariza- Mun,- but;.dis.plays:an equalsignalstrength regardless of the orientation of .a.:receiving dipole in it-hemlanemf :a. fiwavefiront.

tOnecobjectsof :this invention is :to provide an antennafiwhich will radiate :circularly polarized electromagneticzwaves.

:Amither: ohieot :of :the invention is .=to provide "such :an :antenna which ;is :compact in structure iandzeasilyzmamifactured.

:Other objects, ;:advantages, .and znovel features :of :the zinvention will .be :apparent "from :the :de- ;scription herein.

EIn the drawings Fig. 1 displays a preferred embodiment of the :invention; :and

iFig. :2 :displays ."another :preferred embodiment .-:.of ithe: invention.

illig. :3 :illustrates :a avaria'tion of the invention -i1112strated:in jE'ig. 1.

:Fig. ".4 illustrates :another embodiment 50f the invention. V

.EReferring-mowto Fig. 31 :whereingis displayed :a perspective mew of one .-preferred1embo diment. of

the invention,- circularlycsymmetric coaxial cable 118 used :to conduct for guide :energy :to the "antenna proper. zNearthelterminusnfazoaxiallcable iiandielectrically connected [to sits (Olllifil :conducstor tare -fo.ur zracliating elements '1, 8, 2:9, :and 2H] =extending radially outward. fromcconductorrfi. and sspaced :at substantially {equal :angular .intervals .of-.90. Radiating-elements 'landr-t arepaired rand constituteadipole,1 as also -.are radiating :ele- .'-ments zB-and .19. .Betweenltheradiating elements in1outer conductor 5 are cut ;longitudinal:;slots J9, J2, no, and IA lforming-ginter-gslot portions .I-l

l2, l3, and I4. Thus, a radiating element :is {connected-to and:extendsiradiallycoutwards from 84311gintereslottportion El I, zit. I'3,';cr :1 4.

in .mder 1120 :provide :a :means for efficiently sdfiving iradiating elements :1 to I ll :inclusive, *an aelect-rically @confluctive feed element :15 connects iinnercconductor 11% of cable 5totheiinsitle of the zinter-eslotwportionts ofttheouter conductor from ewhich'radiatingselement 1 extends. It Phas been found that connecting the inner and outer coniductors'by a radial member P5 v:as -shown is satisfactory.

The leng'th of slots i H to HI inclusive afiects the phasing of radiation from elements to 4'0 inlengths by experiment.

In the structure displayedin Fig. .1,. itI-hasbeen found that maximumradiationis directed with =very'low gain in the direction of the longitudinal axis-of-coaxial cable '5. Considernowradiation reaching a point in space some distance frcm the; antenna but generally along the extendedaxis of-cablela. It will-be observed that paired-elements 1 and-9 from one dipole and paired elementsBand l E) form another dipole. Each dipole "radiates energy which, due to the orientation thereof, is substantially in space quadrature. Adjustment of the length of slots I l to M inclusive alters the phasing .of "radiation from each .of said dipoles, and also results in variationin the ,relative intensity thereof. "By appropriate ad- 'justment .it is ,possible'to -achieve phase quadraturean'd to;subs'tantially equalize the intensity of .radiationiromeach oi-said dipoles. :Radiaticn .inibothspace and phasequa'clrature with equal .amplitude is thereby provided. The resultant .radiation is thus circularly polarized.

Referring now .to .Fig. .2, a. second embodiment .isshownin=vzhich.a.coaxial.cable .28 has conlconnected toits outer conductor 2| .three radiating elements .22, .23, anclfl which extend radially outward iromcable 28 angularly spaced substantially 1-20intervals ina plane perpendicular t0.th.fi iS=0f G&b16}2. Slots 25, Ethanol-27in .outer conductor 21 are spaced between elements .22 to .724 inclusive, iorming inter-slot portions 153-26 and .21 Elenient 2:2 is: driven-by a-short metallic feed element =28 connecting inter-slot .portion 2-? :oiaouter :conductor 35;! to inner coniductor pf cable 12%]. Toiobtain circular :polar- 'iization, sit haSibGBIhfOlllfld convenient to snake the :lengthrof slot 25, thatsl'ot lying between inter- :slotaportionsflSflandlt' itOWlliChiQSlBSO 'vely are connected =radiating elements 23 :and it which are not-directly driven, toloe substantially onequarter wavelength, Whereas :one oi the other slots,=say 2a, is'sulcstantially lessthan one-quarter wavelength and the =remaining slot 2"! is substantially greater than-one quarter wavelength.

' antenna.

An observer measuring radiation from the antenna of Fig. 2 at a great distance removed therefrom along its axis would find in general elliptically polarized radiation. This is because radiation from radiating elements 22 to 24 inclusive may be considered as having a polarization. aligned with the respective radiating elements, each of which might be viewed as components along two previously chosen mutually perpendicular axes normal to the line of sight of the It is possible under certain conditions to have circular polarization, and the conditions are substantially realizable by adjustment of the length of the slots. Although these lengths may be computed to give the desired effect, it has been found more satisfactory to make experimental observations and adjustments.

Although the embodiments illustrated in Figs. 1 and 2 show the radiating elements located near the terminus of a coaxial cable, the cable may extend beyond the radiating elements. The cable may be terminated by a stub support, that is, a continuation long enough to act electrically as an effective open support but closed at its end, or, as illustrated in Fig. 3, the cable 3L5 may L be continued a greater distance and a multiplicity of sets of radiating elements 32, 34 may be included spaced along the cable to give end fire efiects and thereby increase the directivity of radiation. If the cable is continued, the best results for feeding the radiating elements have been obtained by extending slots 38 and 38 longitudinally an equal distance on each side of the plane of the radiating elements, that is, the

lengths .of the slots are substantially doubled, but

they are closed at both ends. Feed elements 39 correspond to the feed elements [5, 28 in the embodiments shown in Figs. 1 and 2. The radiating elements thus may extend substantially from the longitudinally central part of the inter-slot portions thus formed in the outer conductor. Various adjustments of the lengths of the slots and the lengths of the radiating elements result in the radiation having a polarization of differing degrees of ellipticity.

A further variation of the invention is effected by employing a hollow pipe wave guide 40, Fig. 4 rather than a coaxial cable. Thus, the invention is applicable to any inclosed transmission line including a coaxial cable or a hollow pipe wave guide. In the event that a hollow pipe wave guide is utilized, the feed element 42, may be made adjustable in length in its inward extension from the wave guide 40 toward the axis thereof, and is excited and transmits energy by the electromagnetic fields within the pipe. This adjustment may be effected, for example, by using a feed element 42 having telescoped sections 44, 45 or by having the feed element threaded into and through the outer conductor (or pipe wall) so that the portion of feed element extending outwardly from the outer conductor of the line is inserted into a hollowed out portion of a radiating element. In the hollow pipe wave guide variation, adjustment of the length of the feed element will afiect both phasing and impedance match, and this same type of adjustment may be utilized in the coaxial cable variation in which the feed element transmits energy derived from the fields in the inclosed transmission line without necessarily physically contacting the inner conductor.

It will be apparent to those skilled in the art that many other variations of the invention are possible than those described herein and therefore it is not desired to limit the scope of the in- 4 vention other than in the manner indicated in the accompanying claims.

What is claimed is:

1. In an antenna, the combination including a coaxial cable having a longitudinal axis and having an outer conductor with three longitudinal slots therein at substantially equal angular intervals about said axis forming three inter-slot portions of said conductor, three radiating elements electrically connected to said inter-slot portions and extending radially outward therefrom substantially in one plane at substantially equal angular intervals, and a feed element electrically connected to one of said inter-slot portions and extending radially inward therefrom.

2. In the antenna of claim 1 adapted for use at a contemplated operating wavelength, the combination of claim 1 wherein one of said slots adjoining the said one inter-slot portion to which is connected said feed element is substantially greater than one-quarter said wavelength measured in one longitudinal direction from said plane, the other of said slots adjoining said one interslot portion is substantially less than one quarter said wavelength measured in a like direction, and the third said slot is substantially equal to one quarter said wavelength measured in a like direction from said plane.

3. In an antenna, the combination including a coaxial cable having a longitudinal axis and having an outer conductor with four longitudinal slots therein at substantially equal angular intervals forming four inter-slot portions of said conductor, four radiatingelements electrically connected to said interslot portions and extending radially outward therefrom substantially in one plane at substantially equal angular intervals and a feed element electrically connected to one of said inter-slot portions and extending radially inward therefrom.

4. In the antenna of claim 3 adapted for use at a contemplated operating wavelength, the combination of claim 3, wherein two said slots diametrically opposed to each other are substantially equal to each other and less than one quarter said wavelength measured in one longitudinal direction from said plane, and the other two of said slots are substantially equal to each other and greater than one quarter said wavelength measured in a like direction from said plane.

5. An antenna comprising a wave guide having a longitudinal axis and having at least three longitudinal slots formed therein at substantially equal angular intervals about said axis forming at least three inter-slot portions, at least three radiating elements electrically connected to said inter-slot portions and extending radially outwardly therefrom substantially in one plane at substantially equal angular intervals, and a feed element electrically connected to one of said inter-slot portions and extending inwardly therefrom.

6. The device according to claim 5 wherein one of said slots adjoining the inter-slot portion to which said feed element is connected is substantially greater than one quarter of the operating wave length measured in a longitudinal direction from said plane, the other of said slots adjoining said inter-slot portion is substantially less than one quarter of said wave length measured in the same direction, and the third said slot is substantially equal to one quarter of said wave length measured in the same direction from said plane.

7. An antenna comprising a wave guide having 75 a longitudinal axis and having four longitudinal two of said slots that are diametrically opposed to each other are substantially equal to each other and less than one quarter of the operating wave length measured in one longitudinal direction from said plane, and the other two diametrically opposed slots are substantially equal to each other and greater than one quarter of said wave length measured in a like direction from said plane.

OGER E. CLAPP.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,275,646 Peterson Mar. 10, 1942 2,298,449 Bailey Oct. 13, 1942 2,417,895 Wheeler Mar. 25, 1947 2,444,320 Woodward June 29, 1948 2,455,403 Brown Dec. 7, 1948 2,462,881 Marchetti Mar. 1, 1949 2,465,245 Mabry Mar. 22, 1949 

